| Message ID | 20201203012638.543321-2-ming.lei@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | blk-mq/nvme-loop: use nvme-loop's lock class for addressing lockdep false positive warning | expand |
On 12/3/20 2:26 AM, Ming Lei wrote: > flush_end_io() may be called recursively from some driver, such as > nvme-loop, so lockdep may complain 'possible recursive locking'. > Commit b3c6a5997541("block: Fix a lockdep complaint triggered by > request queue flushing") tried to address this issue by assigning > dynamically allocated per-flush-queue lock class. This solution > adds synchronize_rcu() for each hctx's release handler, and causes > horrible SCSI MQ probe delay(more than half an hour on megaraid sas). > > Add new API of blk_mq_hctx_set_fq_lock_class() for these drivers, so > we just need to use driver specific lock class for avoiding the > lockdep warning of 'possible recursive locking'. > > Tested-by: Kashyap Desai <kashyap.desai@broadcom.com> > Reported-by: Qian Cai <cai@redhat.com> > Cc: Sumit Saxena <sumit.saxena@broadcom.com> > Cc: John Garry <john.garry@huawei.com> > Cc: Kashyap Desai <kashyap.desai@broadcom.com> > Cc: Bart Van Assche <bvanassche@acm.org> > Cc: Hannes Reinecke <hare@suse.de> > Signed-off-by: Ming Lei <ming.lei@redhat.com> > --- > block/blk-flush.c | 25 +++++++++++++++++++++++++ > include/linux/blk-mq.h | 3 +++ > 2 files changed, 28 insertions(+) > > diff --git a/block/blk-flush.c b/block/blk-flush.c > index 9507dcdd5881..bf51588762d8 100644 > --- a/block/blk-flush.c > +++ b/block/blk-flush.c > @@ -490,3 +490,28 @@ void blk_free_flush_queue(struct blk_flush_queue *fq) > kfree(fq->flush_rq); > kfree(fq); > } > + > +/* > + * Allow driver to set its own lock class to fq->mq_flush_lock for > + * avoiding lockdep complaint. > + * > + * flush_end_io() may be called recursively from some driver, such as > + * nvme-loop, so lockdep may complain 'possible recursive locking' because > + * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class > + * key. We need to assign different lock class for these driver's > + * fq->mq_flush_lock for avoiding the lockdep warning. > + * > + * Use dynamically allocated lock class key for each 'blk_flush_queue' > + * instance is over-kill, and more worse it introduces horrible boot delay > + * issue because synchronize_rcu() is implied in lockdep_unregister_key which > + * is called for each hctx release. SCSI probing may synchronously create and > + * destroy lots of MQ request_queues for non-existent devices, and some robot > + * test kernel always enable lockdep option. It is observed that more than half > + * an hour is taken during SCSI MQ probe with per-fq lock class. > + */ > +void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx, > + struct lock_class_key *key) > +{ > + lockdep_set_class(&hctx->fq->mq_flush_lock, key); > +} > +EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class); > diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h > index 794b2a33a2c3..5f639240760e 100644 > --- a/include/linux/blk-mq.h > +++ b/include/linux/blk-mq.h > @@ -5,6 +5,7 @@ > #include <linux/blkdev.h> > #include <linux/sbitmap.h> > #include <linux/srcu.h> > +#include <linux/lockdep.h> > > struct blk_mq_tags; > struct blk_flush_queue; > @@ -594,5 +595,7 @@ static inline void blk_mq_cleanup_rq(struct request *rq) > } > > blk_qc_t blk_mq_submit_bio(struct bio *bio); > +void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx, > + struct lock_class_key *key); > > #endif > Reviewed-by: Hannes Reinecke <hare@suse.de> Cheers, Hannes
diff --git a/block/blk-flush.c b/block/blk-flush.c index 9507dcdd5881..bf51588762d8 100644 --- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -490,3 +490,28 @@ void blk_free_flush_queue(struct blk_flush_queue *fq) kfree(fq->flush_rq); kfree(fq); } + +/* + * Allow driver to set its own lock class to fq->mq_flush_lock for + * avoiding lockdep complaint. + * + * flush_end_io() may be called recursively from some driver, such as + * nvme-loop, so lockdep may complain 'possible recursive locking' because + * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class + * key. We need to assign different lock class for these driver's + * fq->mq_flush_lock for avoiding the lockdep warning. + * + * Use dynamically allocated lock class key for each 'blk_flush_queue' + * instance is over-kill, and more worse it introduces horrible boot delay + * issue because synchronize_rcu() is implied in lockdep_unregister_key which + * is called for each hctx release. SCSI probing may synchronously create and + * destroy lots of MQ request_queues for non-existent devices, and some robot + * test kernel always enable lockdep option. It is observed that more than half + * an hour is taken during SCSI MQ probe with per-fq lock class. + */ +void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx, + struct lock_class_key *key) +{ + lockdep_set_class(&hctx->fq->mq_flush_lock, key); +} +EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class); diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 794b2a33a2c3..5f639240760e 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -5,6 +5,7 @@ #include <linux/blkdev.h> #include <linux/sbitmap.h> #include <linux/srcu.h> +#include <linux/lockdep.h> struct blk_mq_tags; struct blk_flush_queue; @@ -594,5 +595,7 @@ static inline void blk_mq_cleanup_rq(struct request *rq) } blk_qc_t blk_mq_submit_bio(struct bio *bio); +void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx, + struct lock_class_key *key); #endif
flush_end_io() may be called recursively from some driver, such as nvme-loop, so lockdep may complain 'possible recursive locking'. Commit b3c6a5997541("block: Fix a lockdep complaint triggered by request queue flushing") tried to address this issue by assigning dynamically allocated per-flush-queue lock class. This solution adds synchronize_rcu() for each hctx's release handler, and causes horrible SCSI MQ probe delay(more than half an hour on megaraid sas). Add new API of blk_mq_hctx_set_fq_lock_class() for these drivers, so we just need to use driver specific lock class for avoiding the lockdep warning of 'possible recursive locking'. Tested-by: Kashyap Desai <kashyap.desai@broadcom.com> Reported-by: Qian Cai <cai@redhat.com> Cc: Sumit Saxena <sumit.saxena@broadcom.com> Cc: John Garry <john.garry@huawei.com> Cc: Kashyap Desai <kashyap.desai@broadcom.com> Cc: Bart Van Assche <bvanassche@acm.org> Cc: Hannes Reinecke <hare@suse.de> Signed-off-by: Ming Lei <ming.lei@redhat.com> --- block/blk-flush.c | 25 +++++++++++++++++++++++++ include/linux/blk-mq.h | 3 +++ 2 files changed, 28 insertions(+)